Reductant nozzle indentation mount

ABSTRACT

An engine exhaust aftertreatment system including a bend routing an exhaust flow in a curved direction to a straight part. A nozzle is mounted in the bend to introduce a spray of a fluid with a axis of symmetry into the exhaust flow. The axis of symmetry intersects the exhaust flow traveling in the curved direction at a intersection angle of less than 50 degrees.

TECHNICAL FIELD

The present disclosure relates to injecting a reductant in an engine exhaust aftertreatment system, and more particularly to mounting and locating a nozzle to inject the reductant.

BACKGROUND

A selective catalytic reduction (SCR) system may be included in an exhaust treatment or aftertreatment system to remove or reduce nitrous oxide (NOx or NO) emissions coming from the exhaust of an engine. SCR systems use reductants, such as urea. These reductants may form deposits in the aftertreatment system.

PCT Patent Application Publication WO 2009071088 (the '088 publn) discloses aligning an axis of spray from a nozzle injecting reductant with an axis of symmetry of a straight part of an exhaust pipe. The '088 publn, however, may not locate the nozzle in a desired location.

SUMMARY

In one aspect, the present disclosure provides an engine exhaust aftertreatment system including a bend routing an exhaust flow in a curved direction to a straight part. A nozzle is mounted in the bend to introduce a spray of a fluid with a axis of symmetry into the exhaust flow. The axis of symmetry intersects the exhaust flow traveling in the curved direction at an intersection angle between the axis of symmetry and the exhaust flow of less than 50 degrees.

In another aspect the present disclosure provides an engine exhaust aftertreatment system wherein the indentation extends into more than 10% of a depth of the bend. In yet another aspect, the indentation includes an upstream wall with an upstream wall length of at least 10% of a depth of a bend inlet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of an aftertreatment system.

FIG. 2 is a diagrammatic view of a bend of the aftertreatment system from FIG. 1.

FIG. 3 is a cross-sectional view of the bend from FIG. 2.

FIG. 4 is a cross-sectional view of the bend from FIG. 2 showing an exhaust flow and a spray of reductant.

FIG. 5 is a cross-sectional view of a bend and straight part from FIG. 1 showing the distribution of a spray of reductant as it passes down the straight part.

FIG. 6 is a cross-sectional view of a bend and straight part from FIG. 1 showing the distribution of a spray of reductant as it passes down the straight part and through a mixer.

FIG. 7 is a cross-sectional view of the bend from FIG. 2 showing the nozzle mounted at an angle.

DETAILED DESCRIPTION

The aftertreatment system 10 seen in FIG. 1, receives an exhaust flow 12 from an engine or power system. The engine may be any type of engine (internal combustion, gas, diesel, gaseous fuel, natural gas, propane, etc.), may be of any size, with any number of cylinders, and in any configuration (“V,” in-line, radial, etc.). The engine may be used to power any machine or other device, including on-highway trucks or vehicles, off-highway trucks or machines, earth moving equipment, generators, aerospace applications, locomotive applications, marine applications, pumps, stationary equipment, or other engine powered applications.

The aftertreatment system 10 includes an SCR catalyst 14 and a reductant system 16. The SCR catalyst 14 includes a catalyst material disposed on a substrate. The catalyst material is configured to reduce an amount of NOx in the exhaust flow 12 by using a reductant 19. The substrate may consist of cordierite, silicon carbide, other ceramic, or metal. The substrate may include a plurality of through going channels and may form a honeycomb structure. An ammonia oxidation catalyst (AMOX) may also be included downstream of the SCR 14 or zone coated on the end of the SCR 14.

The reductant system 16 includes an injector or nozzle 18 that introduces a reductant 19 into the exhaust flow 12. The nozzle 18 may include springs, washers, cooling passages, injector pins, and other features not shown.

While other reductants 19 are possible, urea is the most common source of reductant 19. Urea reductant 19 decomposes into ammonia (NH3) and is then adsorbed or stored in the SCR catalyst 14.

The exhaust flow 12 is introduced to the SCR catalyst 14 via an exhaust pipe 20. The exhaust pipe 20 includes a straight part 22 and a curved part or bend 24 upstream from the straight part 22. The nozzle 18 is mounted in the bend 24. The length of the straight part 22 or distance between the nozzle 18 and SCR catalyst 14 may be sufficiently long to achieve the mixing of reductant 19 into the exhaust flow 12 and provide the dwell time for the urea reductant 19 to convert into NH3.

The aftertreatment system 10 may also include a diesel oxidation catalyst (DOC) 26, a diesel particulate filter (DPF) 28, and a clean up catalyst or other exhaust treatment devices upstream or downstream of the SCR catalyst 14. The currently illustrated aftertreatment system 10 shows the DOC 26 upstream of the DPF 28, which is upstream of the SCR catalyst 14.

The aftertreatment system 10 may also include a heat source 30 to regenerate the DPF 28. The heat source 30 may embody a burner including a combustion head and a housing to contain a flame. The heat source 30 may also embody an electric heating element, microwave device, or other heat source. Heat may also be created by injecting a hydrocarbon source, such as fuel, in to the exhaust flow 12 that will exothermically react in the DOC 26. The heat source 30 may also embody operating the engine under conditions to generate elevated exhaust flow 12 temperatures.

The DOC 26 and DPF 28 may be housed in a common first canister 32. The DOC 26 and DPF 28 may also be housed in separate canisters. The SCR catalyst 14 may be housed in a second canister 34. The heat source 30, first canister 32, and second canister 34 may be arranged in side-by-side parallel orientation on a mount 36. The heat source 30, first canister 32, and second canister 34 may also be arranged and mounted in other ways.

The exhaust pipe 20 may also include second bend 38 downstream of the straight part 22 for routing the exhaust flow 12 into the second canister 34. In other embodiments, this second bend 38 may not be included and the second canister 34 may be aligned with the straight part 22. The first and second canisters 32 and 34 may also include ends 40 for delivering and receiving the exhaust flow 12.

An entering pipe 42 routes the exhaust flow 12 to the aftertreatment system 10. The second canister 34, or another end canister, may include an exit port 44 for the exhaust flow 12 to exit the aftertreatment system 10.

An additional section of exhaust pipe (not shown) may route the exhaust flow 12 from the heat source 30 to the first canister 32 receiving end 40. In other embodiments, the heat source 30 may not be included and the entering pipe 42 may route the exhaust flow 12 to the first canister 32 receiving end 40.

The exhaust flow 12 passes through the entering pipe 42 and next through the heat source 30, if included, in a first direction 46. Next, the exhaust flow 12 is routed to pass through the first canister 32 in a second direction 48 that may be parallel to the first direction 46. The exhaust flow 12 passes through the DOC 26, DPF 28, end 40, and through the bend 24. Next the exhaust flow 12 passes through the straight part 22 in a third direction 50 that may be parallel to the second direction 48. Next, the exhaust flow 12 is routed to pass through the second bend 38 and through the second canister 34 in a fourth direction 52 that may be parallel to the second direction 48. Finally the exhaust flow 12 exits through the exit port 44.

The reductant system 16 may also include a reductant source 54, pump 56, and valve 57. The reductant 19 is drawn from the reductant source 54 via the pump 56 and delivered to an inlet connection 58 on the nozzle 18. The valve 57 or pump 56 may be used to control the delivery of the reductant 19. A controller and sensors may also be included to control the reductant system 16. The controller and sensors may also control the heat source 30. The controller may also be in communication with an engine control module (ECM) or may be included in the ECM.

The reductant system 16 may also include a coolant source 60 that delivers coolant 62 to the nozzle 18 via coolant ports connections 64. The coolant source 60 may embody the engine's coolant system or another coolant source 60. The coolant 62 may also be used to cool other parts of the reductant system 16 or aftertreatment system 10. The coolant 62 may also be used to thaw frozen urea 19.

Seen best in FIG. 4, the nozzle 18 includes a tip or outlet 66. A spray 68 of reductant 19 is introduced in the exhaust flow 12 from the outlet 66. The spray 68 defines an axis of symmetry 70. Absent any influence by the exhaust flow 12, the axis of symmetry 70 may be substantially parallel to the third direction 50.

Seen best in FIG. 2, the bend 24 includes a bend inlet end 72, bend outlet end 74, bend outer curve 76, bend inner curve 78, and bend sides 80. The bend outer curve 76, bend inner curve 78, and bend sides 80 form a bent tube or box structure with an open bend inlet end 72 and bend outlet end 74. The bend inlet end 72 joins to and is in fluid communication with the end 40 of first canister 32. The bend outlet end 74 joins to and is in fluid communication with the straight part 22.

The bend outer curve 76, bend inner curve 78, and bend sides 80 discussed above represent walls exposed to the exhaust flow 12. As seen in FIGS. 3 and 4, bend 24 may also include double walls 82 outside of these walls. The double walls 82 provide thermal protection from the exhaust flow 12.

An indentation 84 is included in the bend outer curve 76. The indentation 84 is defined by or includes an indentation downstream wall 86, indentation upstream wall 88, and sidewalls 90. The indentation downstream wall 86, indentation upstream wall 88, and sidewalls 90 form a recessed pocket or area in the bend 24. The indentation 84 may have rounded triangular shape with a width at the upstream end greater than a width at the downstream end. The indentation 84 may also have other shapes, including rectangular, cylindrical, or hemispherical.

The straight part 22 includes an upstream end 92, downstream end 94, outer wall 96, inner wall 98, and sides 100 to form a tubular pipe. Straight part 22, and other components, may be wrapped in insulation 102. The upstream end 92 joins to the bend outlet end 74.

Dimensional aspects of the bend 24 and indentation 84 are seen best FIGS. 2 and 3. FIG. 2 shows the bend 24 has an inlet width 101 and an outlet width 103. The width of the bend 24 may decrease from the bend inlet end 72 to bend outlet end 74 resulting in a smaller outlet width 103 than inlet width 101.

As seen in FIG. 3, the bend 24 has an inlet depth 104 and an outlet depth 106. The depth of the bend 24 may increase gradually from the bend inlet end 72 to bend outlet end 74 resulting in a larger outlet depth 106 than inlet depth 104. Because the relative sizes of the inlet width 101 to outlet width 103 and inlet depth 104 to outlet depth 106 vary in opposite relation, a substantially constant flow area may be maintained.

In other embodiments, the width and depth of bend 24 may be constant or vary differently. The outlet depth 106 and outlet width 103 may substantially match the width or diameter of the straight part 22.

A centerline 108, shown in FIG. 3, extends through the center of the bend 24 and may continue through the straight part 22. The indentation 84 extends into the bend 24 and includes a maximum bend extension point 110. The maximum bend extension point 110 may be a point or line where the indentation downstream wall 86 and indentation upstream wall 88 meet. A bend central plane 112 extends through the maximum bend extension point 110 and is normal to the centerline 108. A projected outer curve 114 extends in space over the indentation 84 along the same curvature as the bend outer curve 76.

A projected center depth 116 represents a central depth of the bend 24 if the indentation 84 did not exist. This projected center depth 116 is the depth of the bend 24 along the bend central plane 112 from the inner curve 78, through the maximum bend extension point 110 to the projected outer curve 114.

A minimum center depth 118 represents a central depth of the bend 24 where it is the smallest because of the indentation 84. This minimum center depth 118 is the depth of the bend 24 along the bend central plane 112 from the bend inner curve 78 to the maximum bend extension point 110.

An indentation maximum extension length 120 represents the maximum depth of the indentation 84. This indentation maximum extension length 120 is the length along the bend central plane 112 from the maximum bend extension point 110 to the projected outer curve 114.

The indentation 84 has a downstream wall length 122 and upstream wall length 124. The downstream wall length 122 is the length extending along the downstream wall 86 from the outer curve 76 to the maximum bend extension point 110. The upstream wall length 124 is the length extending along the upstream wall 88 from the outer curve 76 to the maximum bend extension point 110. Although many of the dimensions above are referred to as minimums and maximums, projections and other additional structures should not be considered as included in these dimensions.

FIG. 4 shows the directions of flow of the exhaust flow 12 as it travels through the bend 24 into the straight part 22. The directions of flow include a straight inlet direction 126, straight outlet direction 128, and a central curved direction 130 between the straight inlet direction 126 and straight outlet direction 128. Also included are blocked flows 132 under the upstream wall 88 of the indentation 84. Dead flows 134 also exist downstream of the downstream wall 86 and in the corner where the downstream wall 86 at outer curve 76 meet.

The nozzle 18 may be mounted in the downstream wall 86 to position the outlet 66 and axis of symmetry 70 to align with the centerline 108 as it extends in the straight part 22.

The indentation 84 is also sized to locate the axis of symmetry 70 to intersect with an intermediate direction 136 of the exhaust flow 12. The intermediate direction 136 is the direction of exhaust flow 12 as it begins to straighten into the straight outlet direction 128 from the central curved direction 130. The intermediate direction 136 is the first exhaust flow 12 to intersect the axis of symmetry 70 that is not blocked by the upstream wall 88.

The axis of symmetry 70 intersects the exhaust flow 12 traveling in the intermediate direction 136 at an intersection angle 138 of approximately 30 degrees. In certain embodiments the intersection angle 138 is less than 50, 45, 40, 35, 35, 30, 25, 20, 15, 10, or 5 degrees. In other embodiments the intersection angle 138 is between 5 and 50 degrees, 5 and 35 degrees, 5 and 25 degrees, 20 and 40 degrees, or 20 and 50 degrees. In yet other embodiments the axis of symmetry 70 may intersect the exhaust flow 12 traveling in the straight outlet direction 128 and the intersection angle 138 may be substantially zero.

The intersection angle 138 is achieved by the location and size of the indentation 84 relative to the bend 24. The percentage of indentation maximum extension length 120 compared to the projected center depth 116 represents the degree to which the indentation 84 extends into the depth of the bend 24. The indentation maximum extension length 120 may be approximately 50% of the projected center depth 116. In certain embodiments, the indentation maximum extension length 120 may be at least 60%, 40%, 30%, 20%, or 10% of the projected center depth 116. In other embodiments, the indentation maximum extension length 120 may be between 10% and 80%, 30% and 70%, 40% and 60%, 30% and 60%, or 40% and 70% of the projected center depth 116.

The upstream wall 88 blocks the exhaust flow 12, requiring a long upstream wall length 124 to achieve the intersection angle 138. The upstream wall length 124 may be approximately 70% of the bend inlet depth 104. In certain embodiments, however, the upstream wall length 124 may be at least 80%, 70%, 60%, 50%, 40%, 30%, 20%, or 10% of the bend inlet depth 104. In other embodiments the upstream wall length 124 may be between 10% and 90%, 30% and 90%, 50% and 90%, 40% and 90%, or 40% and 80% of the bend inlet depth 104.

The downstream wall 86 locates the nozzle 18 and connects to the upstream wall 88, thereby requiring a long downstream wall length 122 to achieve the intersection angle 138 and nozzle 18 position. The downstream wall length 122 may be approximately 70% of the bend outlet depth 106. In certain embodiments, however, the downstream wall length 122 may be at least 80%, 70%, 60%, 50%, 40%, 30%, 20%, or 10% of the bend outlet depth 106. In other embodiments the downstream wall length 122 may be between 10% and 90%, 30% and 90%, 50% and 90%, 30% and 80%, or 30% and 70% of the bend outlet depth 106.

The downstream wall length 122 may also provide a flat mounting surface 140 for mounting the nozzle 18. The size or depth of the indentation 84 and downstream wall length 122 and upstream wall length 124 also provides a recessed area for the nozzle to be located. This recessed area may help protect the nozzle 18 and its connections 58, 64.

Backpressure concerns may limit the size of the indentation 84. These concerns may be at least partially addressed by the shape whereby the indentation 84 narrows as it goes deeper into the bend 24. Backpressure concerns may also be addressed by the ratio of inlet and outlet widths 101 and 103 to an indentation width 143 of the indentation 84. The indentation width 143 may be approximately 20% of the bend inlet width 101. In certain embodiments, however, the indentation width 143 may be at least 80%, 70%, 60%, 50%, 40%, 30%, 20%, or 10% of the bend inlet width 101. In other embodiments the indentation width 143 may be between 5% and 90%, 5% and 60%, 5% and 40%, 10% and 30%, or 20% and 40% of the bend inlet width 101. The indentation width 143 may be approximately 40% of the bend outlet width 103. In certain embodiments, however, the indentation width 143 may be at least 80%, 70%, 60%, 50%, 40%, 30%, 20%, or 10% of the bend outlet width 103. In other embodiments the indentation width 143 may be between 5% and 90%, 5% and 70%, 10% and 60%, 20% and 70%, or 20% and 50% of the bend outlet width 103

Other embodiments may utilize a longer nozzle 18 that extends into the exhaust flow 12 to achieve the intersection angle 138. This design however may cause the reductant 19 to overheat and crystallize inside the nozzle 18 as it is now exposed to the hot exhaust flow 12. This embodiment also fails to protect the portion of the nozzle 18 outside the bend 24. This embodiment may also fail to provide a flat mounting surface 140.

FIG. 5 illustrates the flow of droplets 142 as they are injected from nozzle 18 as a spray 68, intersect with the exhaust flow 12, and travel down the straight part 22. Because of the low intersection angle 138, less of an outward force from the exhaust flow 12 is exerted on the spray 68. Accordingly, the droplets 142 may tend towards (because some outward force may still exists), but not impact in a significant way on the outer wall 96. The low intersection angle 138 helps project the droplets down the straight part 22 in a straighter direction than with a higher intersection angle 138 or a smaller indention 84 because the outward force vector exerted by the exhaust flow 12 traveling in the curved direction 130 on the reductant spray 68 is reduced.

FIG. 6 illustrates an embodiment including a mixer 144. As seen, the mixer 144 helps distribute and mix the droplets 142 with the exhaust flow 12. The mixer 144 also helps prevent the droplets 142 from impacting the outer wall 96 by locating the mixer 144 in the straight part 22 before the droplets 142 have significantly tended towards the outer wall 96. Mixing plates, mixing vanes, and baffles may also be added in the straight part 22 or bend 24.

An alternative embodiment is shown in FIG. 7 with the nozzle 18 disposed at a mount angle 150. Because of the mount angle 150, the axis of symmetry 70 is directed toward the inner wall 98, which helps counteract the outward force of the exhaust flow 12 traveling in the central curved direction 130. The mount angle 150 may be defined as the angle between a nozzle plane 152 and a normal plane 154. The nozzle plane 152 is defined normal to the outlet 66 or front face of the nozzle 18 so that the axis of symmetry 70 will be normal to the nozzle plane 152. The normal plane 154 is defined as perpendicular to the straight outlet direction 128 and may also be parallel to the straight inlet direction 126.

The magnitude of the desired mount angle 150 may depend on the degree of the outward force of the exhaust flow 12 traveling in the central curved direction 130. This outward force will depend on the geometries of the bend 24 and indentation 84. The outward force will also change during engine operation as the mass flow of the exhaust flow 12 changes. The mount angle must be large enough to have a meaningful impact but small enough to avoid reductant 19 from impacting and forming deposits on the inner wall 98 during low exhaust flows 12. The mount angle 150 may be approximately 15 degrees. In certain embodiments the mount angle is greater than zero but less than 50, 45, 40, 35, 35, 30, 25, 20, 15, 10, or 5 degrees. In other embodiments the mount angle 150 is between 10 and 30 degrees, 10 and 20 degrees, 20 and 30 degrees, 5 and 20 degrees, or 30 and 50 degrees.

FIG. 7 also shows that the nozzle 18 may be moved on the downstream wall 86 to be closer to the inner wall 98 than the outer wall 96 to avoid reductant 19 from impacting and forming deposits on the inner wall 98. The mount angle 150 may be formed by tilting the upstream wall 88. FIG. 7 also shows that a curve 156 may be added to the upstream wall 88 so that the length of the upstream wall 88 can be maintained.

The mount angle 150 may create a larger intersection angle 138. In such embodiments, the intersection angle may be approximately 45 degrees. In certain such embodiments the mount angle 150 may result in the intersection angle 138 being as high as 90, 80, 70, 60, 50, 40, or 30 degrees is less than 50, 45, 40, 35, 35, 30, 25, 20, 15, 10, or 5 degrees. In other such embodiments the mount angle 150 may result in the intersection angle 138 being between 10 and 90 degrees, 30 and 90 degrees, 40 and 80 degrees, 40 and 60 degrees, or 50 and 80 degrees.

INDUSTRIAL APPLICABILITY

Reductant sprays 68 often form deposits in the aftertreatment system 10. The deposits may form under a number of different conditions and through a number of different mechanisms. Deposits may form when the urea reductant 19 is not quickly decomposed into NH3 and thick layers of urea reductant 19 collect. These layers may build as more and more urea reductant 19 is sprayed or collected, which may have a cooling effect that prevents decomposition into NH3. As a result, the urea reductant 19 sublimates into crystals or otherwise transforms into a solid composition to form the deposit. This composition may consist of biuret (NH2CONHCONH2) or cyanuric acid ((NHCO)3) or another composition depending on temperatures and other conditions.

While the reductant system 16 may or may not be air-assisted, deposits more readily develop in airless reductant systems 16. Airless reductant systems 16 tend to produce reductant sprays 68 with larger droplet sizes than air-assisted reductant systems 16. The larger droplet size in the reductant spray 68 may cause deposit formations. In general, these deposits may form on surfaces of the aftertreatment system 10 where the reductant spray 68 impinges, recirculates, or settles. For example, the deposits may form on the outer wall 96 or around the outlet 66.

These deposits may have negative impacts on the operation of the power system. The deposits may block the exhaust flow 12, causing higher back-pressure and reducing engine and aftertreatment system 10 performance and efficiency. The deposits may also disrupt the flow and mixing of the urea reductant 19 into the exhaust flow 12, thereby reducing the decomposition into NH3 and reducing NOx reduction efficiency. The deposits may also block the outlet 66 or disrupt the reductant spray 68. The formation of the deposits also consumes urea reductant 19, making control of injection harder and potentially reducing NOx reduction efficiency in the SCR 14. The deposits may also corrode components of the aftertreatment system 10 and degrade the structural and thermal properties of the SCR catalyst 14. The deposits may also block channels of the SCR catalyst 14, again reducing NOx reduction efficiency.

The indentation 84 may help prevent the formation of the deposits by directing the droplets 142 or spray 68 down the straight part 22. The low intersection angle 138 created by the downstream and upstream wall 86 and 88 and blocking effect of the upstream wall 88 reduce the amount of reductant 19 impacting the outer wall 96 and may prevent the formation of deposits. Likewise, the mount angle 150 also reduces the amount of reductant 19 impacting the outer wall 96 and may prevent the formation of deposits. The indentation 84 may also reduce recirculation of reductant spray 68 around the outlet 66, preventing formation of deposits around the outlet 66.

The indentation 84 also provides a recessed area or pocket for the nozzle 18 to be located. This recessed area provides a level of protection to the nozzle 18 and reduces the outer size of the aftertreatment system 10 package. The indentation 84 may also provide a flat surface 140 for mounting the nozzle 18.

Although the embodiments of this disclosure as described herein may be incorporated without departing from the scope of the following claims, it will be apparent to those skilled in the art that various modifications and variations can be made. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents. 

1. An engine exhaust aftertreatment system comprising: a bend routing an exhaust flow in a curved direction; a straight part receiving the exhaust flow from the bend; and a nozzle mounted in the bend to introduce a spray of a fluid with a axis of symmetry into the exhaust flow wherein the axis of symmetry intersects the exhaust flow traveling in the curved direction at a intersection angle between the axis of symmetry and the exhaust flow of less than 50 degrees.
 2. The engine exhaust aftertreatment system of claim 1 further including an indentation in the bend wherein the nozzle is mounted in the indentation.
 3. The engine exhaust aftertreatment system of claim 2 wherein the indentation extends into more than 10% of a depth of the bend.
 4. The engine exhaust aftertreatment system of claim 2 wherein the indentation includes an upstream wall with a upstream wall length of at least 10% of a depth of a bend inlet.
 5. The engine exhaust aftertreatment system of claim 4 wherein the indentation includes a downstream wall with a downstream wall length of at least 10% of a depth of a bend outlet.
 6. The engine exhaust aftertreatment system of claim 5 wherein the nozzle is mounted in the downstream wall.
 7. The engine exhaust aftertreatment system of claim 6 wherein the nozzle is located to align the axis of symmetry of the spray with a central axis of the exhaust flow in the straight part.
 8. The engine exhaust aftertreatment system of claim 6 wherein the upstream wall length is at least 50% of a depth of a bend inlet and the downstream wall length is at least 50% of a depth of a bend outlet.
 9. The engine exhaust aftertreatment system of claim 1 wherein the indentation has a triangular shape.
 10. The engine exhaust aftertreatment system of claim 1 wherein the intersection angle is less than 40 degrees.
 11. The engine exhaust aftertreatment system of claim 1 wherein the intersection angle is approximately 30 degrees.
 12. The engine exhaust aftertreatment system of claim 1 further including a selective catalytic reduction system and the fluid is a urea reductant.
 13. An engine exhaust aftertreatment system comprising: a bend routing an exhaust flow in a curved direction; a straight part receiving the exhaust flow from the bend; an indentation extending into more than 10% of a depth of the bend; and a nozzle mounted in the indentation to introduce a spray of a fluid into the exhaust flow.
 14. The engine exhaust aftertreatment system of claim 13 wherein the indentation includes an upstream wall with a upstream wall length of at least 10% of a depth of a bend inlet.
 15. The engine exhaust aftertreatment system of claim 14 wherein the indentation includes a downstream wall with a downstream wall length of at least 10% of a depth of a bend outlet and the nozzle is mounted in the downstream wall.
 16. The engine exhaust aftertreatment system of claim 13 wherein the indentation extends into more than 30% of a depth of the bend.
 17. The engine exhaust aftertreatment system of claim 13 wherein the indentation extends into approximately 50% of a depth of the bend.
 18. An engine exhaust aftertreatment system comprising: a bend routing an exhaust flow in a curved direction; a straight part receiving the exhaust flow from the bend; an indentation including an upstream wall with a upstream wall length of at least 10% of a depth of a bend inlet; and a nozzle mounted in the indentation to introduce a spray of a fluid into the exhaust flow
 19. The engine exhaust aftertreatment system of claim 18 wherein the upstream wall length is at least 40% of a depth of a bend inlet.
 20. The engine exhaust aftertreatment system of claim 18 wherein the upstream wall length is approximately 70% of a depth of a bend inlet. 